Analog signal processing systems frequently employ active analog filters constructed of operational amplifiers (op-amps), resistors, and capacitors. For inexpensive mixed signal integrated circuit (IC) processes such as digital complimentary-symmetry metal-oxide-semiconductor (CMOS), large value integrated resistors typically have a poor manufacturing tolerance (approximately 25%) and a relatively high temperature coefficient of approximately 5000 parts per million per degree Celsius (5000 ppm/.degree.C.).
Referring now to FIG. 1 of the accompanying drawings, there is shown a prior art integrated active resistance-capacitance (RC) filter 100 known as a second order Saylen-Keye active RC low pass filter. Resistors R102, R104, R106 and capacitors C108. C110 control the -3 dB bandwidth of the filter 100, and these resistors are typically integrated on chip as resistor arrays under microprocessor control. These resistor arrays exhibit the problems associated with having the poor manufacturing tolerances, and the -3 dB bandwidth can vary by nearly a full order of magnitude. For active RC filters of this complexity, it is impractical to use external precision resistors as a substitute for the internal diffused resistance. Further disadvantages associated with using theses resistor arrays include the amount of die space required and the relatively high cost of the analog process. Filter circuits, such as the Saylen-Keye filter 100, often require manual tuning, usually in the form of programming, of the resistor arrays at the factory level in order to compensate for variations in the process characteristics. This further drives up the cost and time involved in producing these circuits.
Hence, what is needed is an improved circuit and method of tuning an analog integrated circuit, such as the active RC filter 100, such that the circuit remains impervious to variations in process and temperature and relieves the burden of manual tuning.